1. Field of the Invention
A method to synthesize and control the morphology of tubular carbon nano structures. Different morphologies of tubular carbon such as tubes, cones, nozzles, funnels, and multijunctioned tubes, can be synthesized reliably. The technique is based on the wetting behavior of gallium with carbon in different gas phase growth environments.
2. Description of the Prior Art
The myriad structural manifestations and their material properties have made carbon nanostructures very interesting not only for potential applications but also for understanding carbon at the atomic scale. Several different nano-sized structures of carbon have been investigated intensely. A few of these include single and multi-walled nano tubes, helical nanotubes, cones, horns, conical crystals, micro-trees and nanopipettes. The synthesis methods for carbon tubes with larger inner diameters are of interest for applications in micro-/nano-fluidics. Libera et al. reported hydrothermal synthesis of graphite tubes with higher inner diameters ranging from 70-1300 nm using nickel as a catalyst. They also found that the tubes encapsulated “hydrothermal fluid” and process gases during the growth with a fraction of the tubes also containing inner obstructions reminiscent of bamboo styling due to nickel catalyst. Bando et al., synthesized gallium filled straight nanotubes using thermal evaporation of gallium oxide mixed with carbon. Similar results were obtained with thermal evaporation of gallium nitride powder in the presence of acetylene Pan et al. These gallium filled straight carbon tubes have been projected as nano thermometers.
Nanostructures find unique applications in electronics, optoelectronics, and catalysis due to their high surface to volume ratio, enhanced material characteristics due to quantum confinement effects and the high fraction of chemically similar surface sites. Functionalization of these nanostructures can only be achieved and become useful through the synthesis of bulk quantities of defined structures with controlled composition, crystallinity and morphology. Nanostructures of carbon will be of particular interest for these applications.
Up until now, only advanced tools such as electron beam lithography were able to assemble nanostructures, by selectively transferring nano-building blocks, or by surfactant induced mesoscopic organization, and redox templating synthesis of inorganic metal wires. However, these tools are still too slow and cost-prohibitive for the assembly of large-area nanopipettes of nanomaterials for device fabrication.
The teachings of the above-noted prior art demonstrated an uncontrolled growth process yielding only straight tubes with small inner diameters of only about 30-200 nm. Control of the morphology of the carbon nano tubes was not taught by these known references.